The present invention relates to a device for protecting the seal element of a valve. More particularly, the invention relates to such a device which prevents the seal element from being displaced and damaged under the influence of a large pressure differential existing across the valve.
Many hydraulic systems comprise component parts, such as valves, which in use are subjected to large pressure differentials. Since these valves are often required to open and close against these large pressure differentials, they must include seals which are able to withstand the large pressure differentials. One problem with existing valves is that high pressure differentials may cause the seal to be displaced from its normal position within the valve, and this may necessitate removing the valve so that the seal can be replaced.
Valves which are used in high pressure applications often comprise hard seals, such as metallic or hard plastic seals. However, such seals will usually not seal properly unless they are energized, i.e., forced against their corresponding sealing surfaces, and this energizing force can sometimes be very high. Moreover, such seals commonly require smaller tolerances and relatively precise machining of their corresponding sealing surfaces. Also, hard seals are usually static and therefore do not withstand being moved, such as when the valve is opened and closed. Consequently, such seals must often be replaced after only a few operations of the valve. However, in many instances this is not always possible or convenient, such as when the valve is located hundreds of meters below the surface of the water.
Another kind of seal which is often used in valves is a soft elastomeric seal, such as an O-ring seal. Elastomeric seals will usually seal much better than hard seals since they will deform against their sealing surfaces. However, these seals tend to be extruded out of their grooves when the valve is opened, a tendency which becomes more pronounced when the pressure differential across the seal increases. Also, when the valve is being opened and the valve member is moving away from the valve seat, ambient pressure will tend to force the seal towards the valve seat and thereby obstruct the passage between the valve member and the valve seat.
Elastomeric seals are commonly used in poppet valves, such as those that exist in the male and female parts of undersea hydraulic couplings. These poppet valves are opened by inserting the male part into the female part. Before the valves are opened, the fluid in one of the parts will be at operational pressure and the fluid in the other part will be at ambient pressure or even zero pressure. Consequently, when the poppet valves first start to open, a large pressure differential may exist which can force the seals out of their corresponding grooves. This pressure differential can also cause the seals to become deformed, and if the seals are thereby neutralized, water may pour through the poppet valves at high speed and tear the seals partially or completely out of their grooves. If this happens, the coupling may have to be brought to the surface for repair.